Comments

The answer is yes. It is not hard to do. The only problem is that it can also help. Even if you do hurt them there is a very good chance that the penalty will be for only a few months then they will come back and will rank better. Also Google does not catch all link spam. There is a chance that you will just help them.

As ogletree points out - I think that's the great dilemma. If it was that easy, then we'd all be at the mercy of blackhat's trying to destroy our rankings! That's why there can never be a simple Google penalty for link buying.